Resin Pipe Manufacturing Method and Device

The present invention relates to a method and a device for manufacturing a resin pipe.

As a method for molding a resin pipe by resin injection molding, a gas assist molding method is known which includes injecting a molten resin into a cavity of a mold and subsequently introducing a high-pressure gas, such as a nitrogen gas, into the cavity (see, for example, Patent Document 1). Instead of the high-pressure gas, a solid such as a metal ball or a resin ball may be introduced, as an assist material, into the cavity at a high pressure.

When manufacturing the resin pipe by the resin injection molding using the assist material in this manner, an extra molten resin is discharged from the cavity by the assist material introduced into the cavity. The molten resin discharged from the cavity is then solidified. The solidified resin is, for example, pelletized and reused. However, in order to reuse the resin, a processing step of pelletizing the solidified resin is required, and in the subsequent molding step, the pellets need to be heated and melted, which requires a corresponding amount of energy. In addition, when a reinforcing material such as a reinforcing fiber is mixed in the solidified resin, it is difficult to reuse the resin, and it may be necessary to dispose of the resin in some cases. Therefore, there is room for improvement for more effectively using the resin used in the resin injection molding using the assist material.

Patent Document 1: JP 2003-181868 A

An object of the present invention is to provide a method and a device for manufacturing a resin pipe that can more effectively use a resin in molding the resin pipe by resin injection molding using an assist material.

In order to achieve the above object, according to an aspect of the present invention, there is provided a method for manufacturing a resin pipe by injecting a molten resin from one end portion toward an other end portion of a cavity extending in a mold by an injector, and then introducing a fluid or solid assist material into the cavity to discharge an extra molten resin of the molten resin from the cavity, thereby curing the molten resin in a cylindrical shape remaining in the cavity, the method including: introducing the assist material from the other end portion toward the one end portion of the cavity to cause the extra molten resin discharged from the cavity to flow back into the injector; and injecting the back-flowed molten resin from the one end portion toward the other end portion of the cavity by the injector when manufacturing a next new resin pipe.

According to another aspect of the present invention, there is provided a device for manufacturing a resin pipe, including: a mold including a cavity extending in the mold; an injector including an injection outlet connected to one end portion of the cavity and configured to inject a molten resin from the one end portion toward an other end portion of the cavity; and an assist material injection device configured to introduce a fluid or solid assist material into the cavity filled with the molten resin, in which an introduction outlet of the assist material injection device is connected to the other end portion of the cavity, the assist material is introduced from the other end portion toward the one end portion of the cavity to cause an extra molten resin of the molten resin from the cavity to flow back into the injector, and the back-flowed molten resin is injected from the one end portion toward the other end portion of the cavity by the injector when manufacturing a next new resin pipe.

According to the present invention, the extra molten resin discharged from the cavity by introducing the assist material into the cavity is caused to flow back into the injector and can be used when manufacturing a next new resin pipe. Therefore, the resin to be discarded is suppressed, and the resin can be more effectively reused. This is also advantageous in reducing the energy required for reusing the resin.

A method and a device for manufacturing a resin pipe according to an embodiment of the present invention will be described below based on an embodiment illustrated in the drawings.

The embodiment of a manufacturing deviceof a resin pipe illustrated inincludes an injector, an assist material injection device, and a mold. A resin pipeillustrated inis manufactured using the manufacturing device. The resin pipeis a cylindrical body including a peripheral wallformed by a cured resin R, and includes a pipe passageextending in a longitudinal direction. A dot-dash line CL in the drawings indicates a center line passing through a center of a transverse cross-section of the resin pipe(pipe passage).

Although a size of the resin pipeto be manufactured is not particularly limited, an outer diameter is, for example, about 5 mm or greater and 30 mm or less, and a thickness of the peripheral wallis, for example, about 1 mm or greater and 5 mm or less. The resin pipeincludes reinforcing fibers f scattered in the cured resin R. However, since the reinforcing fibers f are arbitrarily used, it is also possible to manufacture the resin pipein which the reinforcing fibers f are not present in the cured resin R. Note that in the drawings, the reinforcing fibers f are shown in an exaggerated manner.

The injectorincludes a cylinderand a screwprovided inside the cylinder. The injectoris not limited to the type shown in the drawing, and various known resin injection molding machines such as a pre-plasticizing type can be used. An injection pathis connected to an injection outletat a tip of the cylinder. The injection pathis connected to the mold. The resin to be used is heated and melted inside the cylinder, and the molten resin Ris injected from the injection outlettoward the inside of the moldby the rotating (forward rotating) screw.

For the resin used as the molten resin R, an appropriate type of resin is selected from various known resins that can be injected, depending on the performance or the like required for the resin pipe. For example, when manufacturing the resin pipefor an air conditioner to be mounted on an automobile, polyamide, polyphenylene sulfide, polypropylene, ABS resin, or the like is used, and nylon resin (such asnylon) is suitably used.

As the reinforcing fibers S, various fibers (for example, short fibers or long fibers such as glass fibers or carbon fibers) can be mixed at a predetermined ratio (for example, 30% parts by mass or more and 40% parts by mass or less per 100 parts by mass of the resin). The short fibers are sized to have, for example, an outer diameter of about 0.001 mm or greater and 1.0 mm or less and a length of about 0.01 mm or greater and 10 mm or less. In this embodiment, the molten resin Rmixed with reinforcing fibers f is used.

The assist material injection deviceincludes a housing portionin which a fluid (gas or liquid) or solid assist material As is accommodated. As the assist material injection device, various known injection devices can be used. For the assist material As, an appropriate known material is selected from a gas such as nitrogen gas or air, a liquid such as water or oil, or a solid such as a metal ball or a resin ball.

An introduction pathis connected to an introduction outletat a tip of the housing portion. The introduction pathis connected to the mold. The assist material As is introduced from the introduction outlettoward the inside of the moldat a predetermined pressure.

The moldis constituted of one moldA and the other moldB assembled to each other. The moldsA andB are contacted and separated with a parting line PL being a boundary. Although the two-piece moldis used in this embodiment, various other known types of moldscan be used.

A cavitythat is a hollow cavity is formed in the mold. The cavityextends from one end portionto the other end portionin a shape identical to that of the resin pipeto be manufactured. An injection outletis connected to the one end portionof the cavityvia the injection pathand the introduction outletis connected to the other end portionvia the introduction pathThe injection outletmay be indirectly or directly connected to the one end portionof the cavity, and the introduction outletmay be indirectly or directly connected to the other end portionof the cavity.

Next, an example of a procedure of a method for manufacturing the resin pipeusing the manufacturing devicewill be described.

As illustrated in, in a state in which the moldsA andB are assembled to each other and closed, the molten resin Ris injected into the moldby the injector. As illustrated in, the injected molten resin Ris injected from the injection outletinto the cavityvia the injection path. Specifically, the molten resin Ris injected from the one end portiontoward the other end portionof the cavity, and the cavityis filled with the molten resin R. Note that in, the reinforcing fibers f mixed in the molten resin Rare not shown.

Next, the assist material As is introduced into the moldby the assist material injection device. That is, as illustrated in, the assist material As is introduced at a predetermined pressure from the other end portiontoward the one end portionof the cavityfilled with the molten resin R. The introduced assist material As passes through the inside of the cavityalong the extending direction of the cavityat a predetermined pressure.

When the assist material As passes through the inside of the cavity, the extra molten resin Ris discharged from the one end portionof the cavity, and the molten resin Radhering to the cavityremains in a cylindrical shape in the cavity. When the assist material As is introduced from the assist material injection device, the injectorretracts the screwto cause the molten resin Rdischarged from the cavityto flow back into the cylindervia the injection path

As illustrated in, the remaining molten resin Ris cured inside the cavity. Thus, the resin pipeis molded by the cured resin R. Useless portions of the cured resin R(portions that do not form the resin pipe) are integrated with both end portions of the resin pipe.

Next, the moldsA andB are separated at the parting line PL to open the mold, and the molded resin pipeis taken out together with the useless portions of the cured resin R. As a result, the cavityis in an empty state. The resin pipeillustrated inis manufactured by cutting off the useless portions of the cured resin Rfrom the taken out resin pipe.

In the moldin which the cavityis in an empty state, a next new resin pipeis subsequently continuously manufactured. Then, the molten resin Rflowed back into the cylinderis injected from the one end portiontoward the other end portionof the cavityas illustrated inin the same procedure as described above. Next, as illustrated in, the assist material As is introduced at a predetermined pressure from the other end portiontoward the one end portionof the cavityfilled with the molten resin Rin the same procedure as described above. As a result, a new resin pipeis molded, and the extra molten resin Rdischarged from the cavityis caused to flow back into the cylindervia the injection path

In this manufacturing method, the extra molten resin Rdischarged from the cavityby introducing the assist material As into the cavityis caused to flow back into the injectorand can be used when manufacturing a next new resin pipe. Therefore, the resin to be discarded is suppressed, and the resin can be more effectively reused.

If the assist material As is introduced from the one end portiontoward the other end portionof the cavityas in the related art, the molten resin Rdischarged from the cavityis cured as it is without flowing back into the injector. Along with this, a large amount of useless portions of the cured resin Rare generated. However, according to the manufacturing method described above, the amount of useless portions of the cured resin Rcan be suppressed. When the molten resin Rmixed with the reinforcing fibers f is used as in this embodiment, it is difficult to reuse the cured resin Rbecause the reinforcing fibers f are included in the cured resin R. However, the above-described manufacturing method is particularly effective in effectively using the resin without wasting it, and is very effective in suppressing the material (resin) cost in the case of an expensive resin.

In addition, in the above-described manufacturing method, the extra molten resin Rdischarged from the cavityis subsequently used as an injection material in the molding step. Therefore, it is not necessary to perform a processing step of pelletizing the generated useless portions of the cured resin Rin order to reuse the useless portions or to melt the pellets thereafter, which is advantageous in suppressing energy required for reusing the resins.

Although the resin pipemanufactured in the above-described embodiment is a straight pipe in which the pipe passageis linear, the shape of the resin pipeis not particularly limited. Since the resin pipeis molded using the assist material As, it is suitable for manufacturing a non-straight pipe including the pipe passagethat is bent as the resin pipeillustrated in. In the above-described manufacturing method, even the resin pipeincluding a plurality of bent portions can be manufactured with high productivity.